Diesel - Patrol engines, Mobil oil difference

Dear Experts

I have 1996 Prado with 1kz engine , 3000 Diesel Turbo. In first 10 months i used the normal mobil oil that is used for diesel engines from toyota, PSO or shell and it was giving average millage of 5.5 km/litre. 2 month back i went to Total for oil change, the owner of the pump is my friend, he advised me to use semi synthtic oil ( 10 w 40 ) that is usually considered for patrol engines. HE said this will increase ur car milleage and pick. Soon after changing the oil i noticed increase in pick and millage from 5.5 to 6.7km/l. I m happy with this change. I know 10 w 40 oil is thin compared to other diesel engine oils, so instead of changing at 3500km i replaced it at 2500 km.
I just want to confirm from experts that is this ok or this oil harms the engine.

10W-40 is viscosity grade of engine oil. U can also 10W-30. For identification of engine oil whether for gasoline or diesel engine, check API grading like CI-4, CH-4
So check the product which r u using of its API grading
The diesel engine required higher TBN (Total Base Number) then gasoline engine oil.

I have 1996 Prado with 1kz engine , 3000 Diesel Turbo. In first 10 months i used the normal mobil oil that is used for diesel engines from toyota, PSO or shell and it was giving average millage of 5.5 km/litre. 2 month back i went to Total for oil change, the owner of the pump is my friend, he advised me to use semi synthtic oil ( 10 w 40 ) that is usually considered for patrol engines. HE said this will increase ur car milleage and pick. Soon after changing the oil i noticed increase in pick and millage from 5.5 to 6.7km/l. I m happy with this change. I know 10 w 40 oil is thin compared to other diesel engine oils, so instead of changing at 3500km i replaced it at 2500 km.
I just want to confirm from experts that is this ok or this oil harms the engine.

I have 1996 Prado with 1kz engine , 3000 Diesel Turbo. In first 10 months i used the normal mobil oil that is used for diesel engines from toyota, PSO or shell and it was giving average millage of 5.5 km/litre. 2 month back i went to Total for oil change, the owner of the pump is my friend, he advised me to use semi synthtic oil ( 10 w 40 ) that is usually considered for patrol engines. HE said this will increase ur car milleage and pick. Soon after changing the oil i noticed increase in pick and millage from 5.5 to 6.7km/l. I m happy with this change. I know 10 w 40 oil is thin compared to other diesel engine oils, so instead of changing at 3500km i replaced it at 2500 km.
I just want to confirm from experts that is this ok or this oil harms the engine.

Regards

Asad Sethi

It will not harm your engine. The reason why you are probably seeing an increase in mileage is because you were using 20w50 oil before. Now you've gone to a thinner oil which will give your engine parts lesser friction due to the lower viscosity (fluid friction). Changing oil at 2500km, that too semi-synthetic oil, is an overkill. You should be just fine at changing at 5,000km intervals.

Rao.

I will miss her, that RKR. She will always be the one that got away.
But, life goes on. From RKR to MMC. 4x4 Engaged? Team Unimog, Pakistan